The present invention relates to a dual compensation intended to be used in a dual hydraulic brake circuit of a motor vehicle.
Such compensators are used in motor vehicles, in order to make it possible to modulate the hydraulic pressure exerted on the rear-wheel brake motors as a function of the load on the rear axle. These compensators consist conventionally of a valve subjected to the action of a calibrated spring in order to protect the rear circuit from any increase of pressure above a predetermined value. The calibration of the spring is variable as a function of the load experienced by the rear undercarriage of the vehicle by means of a lever which is mounted pivotably on a pivot pin fastened to the compensator and the position of which represents the distance between a body element and an element of the rear undercarriage.
U.S. Pat. No. 4,101,176 makes known a dual brake corrector comprising, in a single housing, two correcting valves, of which the inlets are intended to be connected separately to two independent brake-pressure sources and the outlets to two independent sets of brake motors, each correcting valve being capable of controlling the values of pressures at its inlet and at its outlet according to a predetermined relation and comprising a piston subjected to elastic return means. In this dual corrector, a mechanical control is arranged between the pistons of the correcting valves and the elastic means, the inlet member of the mechanical control being subjected to the force generated by the elastic return means, while the outlet members interact separately with the pistons of the two correcting valves.
In the event of complete failure of one of the brake circuits associated with one of the correcting valves, the brake pressure is modified in the intact circuit in an adjustable way and can even be doubled. The failure of a circuit is thus overcome, enabling the driver of the vehicle to stop the latter, while this failure of a circuit is also signalled to the driver by a pressure-drop indicator of known type.
Such correctors thus act as safety systems in the event of a failure in a circuit, but it can happen that these correctors themselves fail and that this failure is not signalled to the driver. This will occur, for example, when the elastic return means is broken or relaxed, the inlet member of the mechanical control has seized, one of the shutters does not close or shows leaks, etc.